1. Field of the Invention
This invention is directed to a system and attendant apparatus operative to establish a variable operative fuel mixture for powering a stationary engine or generator, as well as a vehicle engine. The operative fuel mixture may comprise a varying ratio of both a gaseous fuel, such as natural gas, and a distillate fuel, such as diesel. The ratio of gaseous and distillate fuel is dependent, at least in part, on a plurality of operating characteristics of the engine, which are monitored by an electronic control unit (ECU). The system is adaptable for determining an efficient and effective operative fuel mixture due at least partially to the inclusion of one or more mixing assemblies each comprising and integrated throttle body and air-gas mixer.
2. Description of the Related Art
Typically large, stationary engines as well as mobile engines used to power heavy duty industrial vehicles are powered by either direct drive diesel or diesel electric power trains frequently including a multiple horse power turbo charged operation.
Accordingly, it is well recognized that distillate fuels, specifically diesel, are used as the primary fuel source for such engines. Attempts to maximize the operational efficiency, while maintaining reasonable safety standards, have previously involved modified throttle control facilities. These attempts serve to diminish adverse effects of control mechanisms which may be potentially harmful to the engine operation and may also be at least generally uneconomical. Typical adverse effects include increased fuel consumption and wear on operative components. Therefore, many diesel engines are expected to accommodate various types of high capacity loads and provide maximum power for relatively significant periods of operation. As a result, many diesel engines are commonly operated at maximum or near maximum capacity resulting in an attempted maximum power delivery from the engine and consequent high rates of diesel consumption. It is generally recognized that the provision of a substantially rich fuel mixture in the cylinders of a diesel engine is necessary for providing maximum power when required. Such continued high capacity operation of the engine results not only in wear on the engine components, but also in high fuel consumption rates, lower operating efficiencies, more frequent oil changes and higher costs of operation.
Accordingly, there is a long recognized need for a fuel control system specifically intended for use with high capacity, variable or constant speed compression ignition engines that would allow the use of more efficient fueling methods using other commonly available fuel sources. Therefore, an improved fuel control system is proposed which is determinative of an effective and efficient operative fuel mixture comprised of a combination of gaseous and distillate fuels. More specifically, gaseous fuels can comprise a natural gas or other appropriate gaseous type fuels, wherein distillate fuel would typically include, but not be limited to diesel fuel.
Such a preferred and proposed fuel control system should be capable of regulating the composition of the operative fuel mixture on which the engine operates to include 100% distillate fuel, when the operating mode(s) thereof clearly indicate that the combination of gaseous and distillate fuels is not advantageous. Further, such a proposed fuel control system could have an included secondary function to act as a general safety system serving to monitor critical engine operating parameters. As a result, control facilities associated with such a preferred fuel control system should allow for discrete, user defined control and safety set points for various engine and/or fuel system parameters.
In order to enhance efficient operation of an engine it is known to use a mass air flow sensor to determine the mass flow rate of air entering an internal combustion engine. It is known that air changes its density as it expands and contracts with temperature and pressure. As a result, it has been found that the determination of mass air flow is more appropriate than volumetric flow sensors for accurately determining the quantity of intake air delivered to the combustion section of the engine.
In the proper operation of CI engines, other factors to be considered include, but are not limited to, the occurrence of engine knocking. Knocking is a common occurrence in diesel engines where fuel is injected into highly compressed air at the end of the compression stroke. There is a short lag between the fuel being injected and combustion starting. Typically there is a quantity of fuel in the combustion chamber which will be ignited first in areas of greater oxygen density prior to the combustion of the complete fuel charge. A sudden increase in pressure and temperature may cause what has been recognized as a distinctive diesel “knock” or “clatter”.
Yet another factor to be considered in the effective and efficient performance of CI engines is “flammability limits”. Flammability limits refer to the fact that mixtures of gaseous fuel and air will only burn if the fuel concentration lies within well defined limits. The terms “flammability limits” and “explosive limits” are used interchangeably and recognized flammability limits are typically determined experimentally. Maintaining a preferred combination of fuel and air in an explosive mixture is important in internal combustion engines specifically including, but not limited to, CI engines or diesel engines. In addition, it is important to maintain the air fuel mixture below “lower flammability limits” prior to the delivery of the air fuel mixture into the combustion chambers in order to avoid or restrict pre-ignition and resultant damage to the engine.
Another known characteristic of CI or diesel engines is the establishment of a single safety set point occurring at maximum load conditions of the engine. However, due to the fluctuation of engine performance in the variable range of loads at which the engine operates, the proposed improvement in the functionality of CI engines would be the establishment of a system capable of dynamic set point protection. More specifically, a proposed system which may be originally included or retrofitted into a diesel engine would be the inclusion of structural and operative features which allows the CI engine to operate on a variable mixture of gaseous and distillate fuel. Moreover, under such operating conditions dynamic set point protection would comprise the ability to monitor engine performance across a variable range of engine loads and in association therewith determine a plurality of discrete safety and control set point values. As such, the determination of safety and control set point values would result in either engine shut-off or a deactivation of a gaseous/distillate operative mode and a transition to a full distillate operative mode when the responding safety and/or control set points indicate that engine shut off and/or 100% diesel mode operation is appropriate.